Gardeners’ Chronicle, ser. 3, 35:29 (January 2, 1904), 35: 35 (January 16, 2004)

(The Theory of Functional Capacity and its Results in Agriculture.)
Studies in Applied Vegetable Anatomy and Physiology.
By Lucien Daniel, Professor of Applied Botany at the University of Rennes.*

*lmprimerie Fr. Simon, successeur de A. Le Roy, Rennes, France, 1902. Price 20 francs.

THIS is one of those excellent treatises of the author containing the results of his experiences in applying an adequate knowledge of botanical anatomy and physiology to the common everyday practical work of horticulture. All gardening practices, however simple, e.g., the growing of Mustard-and-Cress or Cabbages, require, in order to be successful, a certain amount of scientific knowledge, although this latter is often unconsciously inherited or otherwise transmitted. The florist or kitchen gardener may boast his independence of, and sheer contempt for, this scientific knowledge; while all the time he is (consciously or unconsciously) possessing and using it. Few indeed are the intelligent men, especially in this country, who are able to keeps fully conscious eye and mind directed to both the scientific and practical aspects of horticulture. How much more might be accomplished than is accomplished if a wider and a deeper scientific knowledge could be mingled with our hackneyed and rule-of-thumb operations in the garden!

The general nutrition of a plant depends on the due proportion between root-action and leaf-action in the living plant, in other words on the proper distribution of the sap between the roots and the foliar organs, the two chief factors herein concerned being (1) the total absorption from the external surrounding, or what our author terms the "functional capacity of absorption," denoted by the formula ca; and (2) the total consumption at the points where the sap is used up, or the "functional capacity of consumption," cv.

When the plant is in complete equilibrium as regards its general nutrition, the relation =1 is obtained, i.e., the condition in which consumption and absorption are equal. But under the influence of natural or artificial variations in the external circumstances, or in the respective dimensions of the aerial or subterranean apparatus of the plant; this equilibrium may become upset.

The absence of equilibrium in the nutrition, >1, or the condition in which the aerial consumption is greater than the (usually) subterranean absorption, will correspond to growth in a dry or poor soil; the absence of equilibrium, <1, or the condition in which the absorption is greater than the consumption, will correspond to growth in a moist or rich soil.

In the first case, seeing that the leaves and young shoots are the chief organs concerned in the consumption of the sap, and the roots are those occupied in its absorption, it is evident that the activity of the former overrides that of the latter—i.e., that the leaves consume more than the roots absorb. So that, a order to restore the balance transpiration must be reduced by diminishing the leaf-surface of the plant, and absorption enhanced by increasing the production of roots; and this latter will probably result in some measure from the former. In the second of our two cases the reverse process must take place. If the limits of desiccation or inanition on the one hand, and of watery repletion or indigestion on the other, be passed, the plant must die. It is invariably found that slightly accentuated changes in the media in which the plants grow induce a partial diminution in their normal resistance to parasites. A drier medium is favourable to the action of animal parasites; a moister medium contributes to the more rapid development of vegetable parasites, especially those of a cryptogamic nature.

The absolute value of the "functional capacity" of a given plant—i.e., the capacity of its leaves, &c., to assimilate, or of its roots to absorb, is shown especially in trees under cultivation, in the relative thickness of the wood formed at the moment under consideration, in the relative diameter of the vessels, and the thickness of the cell-membranes.

The boughs, branches, and buds, e.g., of a Pear-tree, possess functional capacities depending on the rapidity of arrival of the sap and the number of vessels engaged in conveying this latter, these two factors themselves bearing a definite relation (1) to the successive angles which the organ (branch or bud) makes with the vertical; (2) to the facilities afforded for the performance of its vegetative functions.

Hence arises a distinction between the form and structure of woody and of fruiting branches, as also the possibility of creating transitions between the two by inducing a rational variation in their functional capacities. The fruiting branch, with its smaller draught of sap, is distinguished from the woody branch by a diminution in its woody conducting tissues, and by an increase in its cellular or spongy tissues and starch-production. For example, if a transverse section be taken below the level of insertion of, say, three branches or twigs whose functional capacities are of a very different nature (e.g., vigorous and vegetative, or weak and fruit-bearing), the hard woody tissue will often be found to be divided up into islands, the respective dimensions of which are, proportional to the functional capacity of the organs (twigs) to which they correspond and below which they occur.

This is proof of the correctness of the theory of functional capacity, which can also be experimentally verified by means of various horticultural practices based either on an increase or diminution in the absolute value of the normal points at which a draught on sap is effected (as in forcing, and the various methods of training branches, &c.), or on variations in their number (different kinds of rationally performed mutilations, &c.).

When an inequality in the work of the members (leaves, &c.), going on at the surface of an organ is artificially provoked (as in one-sided illumination, local wounding of the cortex, unilateral suppression of the roots, buds and leaves, &c.), or if the work of a lateral is transformed into that of a terminal member (as in various methods of pruning and grafting, &c.), the phenomenon of "dorsiventrality" appears, which is faithfully registered in the formation of the secondary wood of the plant or organ concerned.

Another phenomenon to be noticed is the following: If a sudden decrease or increase in the functional capacity of an organ be brought about by cutting or breaking the latter during the period of active growth, this will be registered in the annual zone of secondary wood by the formation of as many zones of harder or softer wood as there have been successive fractures or loppings.

THE author's theory of "functional capacities" is not only capable of explaining the variations in the form and structure of the isolated individual plant, but also a number of phenomena which are to be observed in grafting, i.e., in plants which are caused to live associated together by the will of the grafter.

Now, amongst the effects of the grafting process we have to distinguish those resulting from cicatrisation or healing of the wound, and those proceeding from the fundamental relationships existing between the functional capabilities peculiar to the grafted plants (stock and scion).

The author points out that the scar of cicatrication causes a fatal change in the conduction of the sap, because of the fact that cellular tissue becomes intercalated between the conducting tissues of the stock and the scion, and because the conducting tissues which eventually unite these two latter are comparatively few in number and more or less contorted. The sap passing along them will, therefore, be modified both in quantity and quality. This is, for the scion, equivalent to existence in a drier and poorer medium than the normal. This was demonstrated by grafting the black Belgian Haricot Bean, which is a dwarf form, on that of Soissons, of taller habit and greater functional capacity; in this case the development of the scum is always more insignificant than that of a normal ungrafted control-specimen, this being due to the fact that the tissues of stock and scion unite with difficulty.

With regard to the second of the two effects of grafting above-mentioned, we have to distinguish between (1) the grafting of a plant of greater functional capacity upon a plant possessing this latter in a lees degree, i.e., the case represented by >1; (2) the grafting of a plant of smaller upon a plant of greater functional capacity, i.e., the case represented by <1.

In the first case, to the effect produced by the primary inequality in the respective functional capacities is added that of the scar of cicatrisation, so that the two work harmoniously together towards producing the condition of existence in a medium drier or poorer than the normal. A striking example of this state of things is afforded by grafting the Forget-me-Not (Myosotis palustris) upon the Heliotrope. The functional capacity of the former is very high, i.e., it has need, as its specific name indicates, of a large amount of water; the stock plant, on the contrary, as the hard wood constituting its conducting-system reveals to us, lives in a dry soil, and hence cannot furnish the necessary water to the scion, which, therefore, rapidly blackens and perishes. But if the limit of desiccation causing death be not attained, the variations characteristic of growth an a dry or poor soil will be exhibited, such as diminution in size modifications in the period and character of flowering, hastening of sexual maturity, improvement in the fruit and tubers. increase in hardness of the tissues, decrease in the resistance offered to parasites, shortening of life, &c.

In the second case it is clear that the effects resulting from the scar and from the difference in the functional capacities of stock and scion are in disharmony. The former may override the latter, as in the case of the Haricot Beans mentioned above. A good example of this is seen in the case of the Deadly Night-shade grafted on the giant Tobacco-plant; although the latter possesses a much greater functional capacity, i.e., greater absorptive power, than the former, the scion grows into a dwarfed and almost stem-less specimen, due to the fact that the affinities of the two plants are not sufficiently close to admit of a proper union of their tissues, hence defective cicatrisation and osmosis result. Yet the Belladonna "takes" easily on the Egg-plant or Tomato. But should the graft "take" well the reverse will be the case, and stock and scion will therefore inevitably be situated in the equivalent of a moist rich medium, and will continue to live if the limit of watery repletion is not passed. An example of this is afforded by the grafting of the French Vine upon an American variety, the other conditions of soil and climate being suitable, Under these conditions the variations characteristic of growth in a moist, rich soil will be shown, e.g., increase in size, changes in the mode of flowering, retardation of sexual maturity, lessening of the quality of fruit, increase of liability to cryptogamic diseases, diminution in the amount of stereome or woody tissue, and rounding-off of the prominences in angular stems, &c. Many interesting examples of these axe given.

It must be understood, of course, that the intensity of the effects resulting from these two inverse cases of variation will vary with the character of the soar of cicatrisatlon and the primary value of the functional capacities of the plants concerned, as also with the conditions of the external medium of soil and air. The latter have naturally a more pronounced effect upon the grafted than upon the normal plant.

The author shows besides that the resultant of the effects brought about by the scar of cicatrisation and the functional capacities of the grafted plants will vary with the age of the plant (senility or youth), the kind of medium in which it has lived (health, bringing-up). as also with the hereditary functional capacity of the organ which is chosen as stock or scion (adaptation to the function of forming reserves, natural etiolation, geotropism, adaptation to wood or fruit production, &c.

All these data have a special practical interest as furnishing the gardener with the opportunity of making a rational choice of stocks and scions by resting that choice upon a measurable scientific basis. And, what is of great importance, they, afford the opportunity of foreseeing the modifications in the habit, &c., induced by the process of grafting between plants the characters of which are known, and of treating the same in a rational manner, viz., by combining systems of pruning and manure-outlay, while bearing in mind the value of the relationship cv/ca in the particular medium under consideration.

The evil effects of a grafting operation in which the absolute value of the relationship 1 is exaggerated can be modified by employing the process of mixed grafting; if, e.g., it happens that the consumption of sap is greater than its absorption, one method of increasing the latter is that of allowing adventitious roots to develop on the scion, which then is enabled to receive crude sap along two distinct avenues; as in the case of old Apple-trees when the adventitious roots of the scions were observed to penetrate the decomposed wood of the stock and to exist then as if in solid earth.

Another method consists in inserting one and the same scion on two or more different stocks. If, on the other hand, it happens that the absorption is greater than the consumption, the methods of restoring this disturbance in the equilibrium of nutrition will be the inverse of the preceding. The following experiment is forcible in this connection: Vernonia praealta was grafted on seedlings of Xanthium macrocarpum; when the ordinary method was employed, viz., by radically suppressing all the supplementary shoots sent up by the stock, the scions inevitably died, but when, on the contrary, these supplementary shoots of the stock were maintained, i.e., when the process of mixed grafting was employed, the scions "took." In this case the small degree of consumption by the scion caused by inefficient union of the two plants is supplemented by that of the shoots from the stock, hence equilibrium is restored, and aqueous repletion of the stock, causing the death of the scion, prevented.

Another method consists in "multiple grafting," where several scions of the same varieties or of varieties of different species are inserted on the same stock. In this case each scion will be subjected to the conditions peculiar to its relationship and to a variation with regard to the way in which its fellow-scions comport themselves in relation to ca, i.e., to the stock charged with providing the nutrition common to all. Experimentation shows that it is the scion exhibiting a relationship equal or approaching to unity which ends by gaining the upper hand and annihilating the rest,. On one of three equal shoots of Anthemis frutescens were grafted three equal scions taken from three plants differing more or less as to their functional capacities: Tanacetum Balsamita, Leucanthemum, and Artemisia Absinthium.

From the commencement it was found that Tanacetum "took" better than Leucanthemum, while Artemisia Absinthium was the worst in this respect. Owing to the discrepancy in the union and in the functional capacities of the three scions, the sap from the common stock was distributed proportionally to the respective values of the new areas of consumption. The aforesaid discrepancy will continue to increase until the life of the scions of Leucanthemum and Artemisia will at length be equivalent to that in a soil becoming ever drier and drier, resulting finally in complete desiccation. The Tanacetum, on the other hand, will grow healthily ahead.

The above is an interesting practical case, and has important bearings.  

In conclusion, the author states that "the theory of sap-draining areas (points d'appel) and of functional capacities can alone explain the effects of the various operations performed in agriculture (pruning, grafting, &c.), and of deducing in a rational manner practical applications therefrom."

"It explains, besides, quite as easily the variations in structure observed in normal plants as a result of the variations produced by the external medium during the performance of their functions."

Besides numerous figures in the text, there are twenty plates containing photographs of transverse and other sections of stems, showing how the effects of operations and other variations from the normal life-history of the plant or plants concerned are registered accurately in the structure of the wood. W. C. W.

Daniel bibliography